1. Field of the Invention
This invention relates to an electrolyte containing a polymer compound and light metal salt, a process for producing the same and a battery using the same, and a electrolyte compound.
2. Description of the Related Art
Recently, portable electric products, such as a camcorder (video tape recorder), a cellular phone, and a laptop computer, are spreading quickly. Such electric products require even higher performance of their electrochemistry devices.
Conventionally, in electrochemistry devices such as a secondary battery, liquid electrolyte solution, such as water and organic solvent, have been used as electrolyte to control ion conduction. However, since a liquid electrolyte has problems such as leaking, it is necessary to secure liquid-tightness by using a metal container. Therefore, an electrochemistry device generally becomes heavier and has the less versatility of possible form features. Furthermore, the sealing process is usually complicated. In contrast, the so-called solid electrolyte which consists of an solid state electrolyte has no liquid leak. The solid electrolyte has several other advantages, that is, simplified sealing process, lighter device, and the flexibility of the form selection due to the excellent ability of polymer to be molded into films. Therefore, a lot of researches have been made on the solid electrolyte.
Generally this solid electrolyte consists of a matrix polymer and electrolyte salt from which ion can be dissociated. The matrix polymer has ion dissociation power and has two functions: keeping this ion conductive solid in solid state and behaving as a solvent for electrolyte salt. Armand et al. of the Grenoble University (France) made a report on an example of the solid electrolytes in 1978; they achieved the ion conductivity of the order of 1×10−7 S/cm in a system where lithium perchlorate was dissolved in polyethylene oxide. Since then, a variety of polymer materials are still examined actively, especially a polymer with a polyether structure.
The solid electrolyte such as the polyethylene oxide uses a linear polyether as a matrix. This type of solid electrolyte achieves its ion conductivity by transferring the dissociated ions in the amorphous phase at the temperature above the glass transition point of the matrix polymer using the local segment movement of a polymer chain.
However, the ions dissociated into the linear matrix of a polyethylene oxide which has partially crystalline phase, especially cations are strongly coordinated by the interaction with the polymer chain, and becomes a pseudo-bridge point. This causes partial crystallization, which reduces the segment movement. In order to increase ion conductivity under room temperature, it is necessary to increase the ion dissociation power of the electrolyte salt and to develop a desirable molecular design for the polymer so that the polymer has many amorphous domains where the ions can move easily within a matrix, and the glass transition point of the polymer is kept lower.
In one molecular design, a branch structure is introduced into the polyethylene oxide frame in an attempt to increase ion conductivity (Masayoshi Watanabe, Netsu Sokutei 24 (1) pp 12–21, 1996). However, the synthesis of this type of polymer requires a complicated process.
In another molecular design, a three-dimensional network is introduced into a matrix polymer in an attempt to prevent the crystallization of polymer. This molecular design is applied to, for example, a polymer obtained by polymerizing the acrylic or methacrylic system monomer with a polyoxyalkylene component, as disclosed in Japanese Non-examined Patent Publication No. 5-25353. However, since alkali metal salt is not dissolved in a monomer very well, sufficient ion conductivity can not be achieved. Therefore, it is necessary to obtain an alternative solid electrolyte.